From: Unmasking Masks in Makkah: Preventing Influenza at Hajj Figure 1. Comparison between mask and control groups in randomized controlled trials. Abbreviations: CI, confidence interval; df, degrees of freedom; M-H, Mantel–Haenszel. From: Unmasking Masks in Makkah: Preventing Influenza at Hajj Clin Infect Dis. 2012;54(1):151-153. doi:10.1093/cid/cir826 Clin Infect Dis | © The Author 2011. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com. 1